Attitude control of spacecraft using internal momentum exchange devices

This dissertation addresses some of the important problems related to spacecraft attitude control using internal momentum exchange devices such as Control Moment Gyros (CMGs), reaction wheels and robot manipulators. The use of momentum exchange devices for attitude control is an attractive alternative to reaction type devices such as thrusters due to the fact that they do not require any expendable fuel resources. The batteries needed to run the motors for these momentum exchange devices can be recharged by the solar panels attached to the spacecraft. However, the use of momentum exchange devices has some inherent limitations which are examined in this dissertation.; CMGs have a number of attractive features over other types of momentum exchange devices, such as reaction wheels and manipulator arms, due primarily to their compact construction and torque amplification properties. Their main disadvantage is the presence of singular configurations where the CMGs lose the ability to produce torque in a particular direction. Two methods for handling singularities are proposed in this dissertation. The first is based on a reference motion tracking technique involving the use of feedback to follow a pre-determined maneuver path which is specifically designed to avoid singularities. The second approach involves a steering law which does not avoid singularities, but is valid even when the CMGs are in a singular configuration.; The use of momentum exchange devices for spacecraft attitude control is especially challenging in the presence of disturbances. This dissertation presents a nonlinear variable structure approach to handling disturbances and ensuring global stability for spacecraft in low-earth orbit. Finally, the use of manipulator arms for spacecraft attitude control is addressed. This problem is challenging because the equations describing the motion of the spacecraft and the arms do not satisfy the algebraic conditions for controllability. Hence traditional feedback techniques cannot be used to simultaneously control the arms as well as the spacecraft attitude. This dissertation develops some simple sub-optimal as well as near-optimal methods for simultaneous control of the spacecraft attitude as well as the manipulator arms.